The present invention deals with a design of a vacuum fluorescent display power supply with a regulated display voltage and a regulated power for the filaments.
The approach taken was to use a pulse width modulated power supply as described in SAE Paper 830046, "High Efficiency Low Cost Vacuum Fluorescent Display Power Supply", authored by the inventor.
The improvement presented with the subject invention is to reduce the cost of the system by eliminating the regulator integrated circuit and utilize power from a microcomputer employed for other purposes in the environment of an instrument panel of an automobile.
It is an object of the subject invention to provide a pulse width modulation switching regulator employing a microcomputer to present a minimum pulse width signal to some comparator means such as a software controlled Analog-to-Digital (A/D) converter.
It is a further object of the present invention to employ some comparator means such as a software controlled A/D converter to read the result of a filtered pulse width signal and compare it to a reference and send a signal to the microcomputer to increase the pulse width by one increment if the input is less than the reference.
It is another object of the present invention to employ the same A/D converter or comparator means to read the result of a filtered input pulse width signal and compare it to a reference signal, and to cause the microcomputer to decrease the pulse width by one increment if the input to the A/D converter is greater than the reference signal.
It is still a further object of the subject invention to monitor the filtered pulse width and stabilize it around a reference signal such that the vacuum fluorescent display power supply output voltage is regulated.